This invention relates to ultrasonic surgical devices. The invention also relates to an associated surgical method. The invention is particularly useful in reducing electrical interference between the electromechanical energization system of an ultrasonic surgical device and intraoperative neurophysiological monitoring devices (IONM).
The ultrasonic removal of tissue as a result of direct instrument-target tissue contact is performed with the help of a hand-held device including a handpiece and any of a multitude of handpiece attachments or probes.
In the handpiece, a high voltage signal of a frequency equal to that of the resonant frequency of the handpiece-probe assembly is converted into mechanical vibratory motion. The electromechanical conversion is achieved by using either a magnetostrictive or piezoelectric stack. Typically a handpiece is fitted with a piezoelectric stack.
A piezoelectric stack can be built using one or more piezo-ceramic disks. The ceramic disks are sandwiched between electrodes which ensure an electrical connection to an ultrasonic generator via a handpiece cable.
Ultrasonic systems used for the removal of tissue located in the close proximity of critical structures that are part of the body's nervous system may use an electrical scheme where the piezoelectric stack is electrically isolated from the probe, the applied part. This is called a floating output and is done in order to minimize unwanted leakage currents that could negatively impact the nervous system. However it is noted that leakage current levels that are well within the limits defined by safety standards may create electrical interference with other devices within the surgical field. Such other devices include Intraoperative Neurophysiological Monitoring devices or IONM devices.
Intraoperative neurophysiological monitoring has been utilized in attempts to minimize neurological morbidity from operative manipulations. The goal of such monitoring is to identify changes in brain, spinal cord and peripheral nerve function prior to irreversible damage. Intraoperative monitoring also has been effective in localizing anatomical structures, including peripheral nerves and sensorimotor cortex, which helps guide the surgeon during dissection.
During the ultrasonic removal of tissue via direct probe-tissue contact, leakage currents, even when below the safe operating levels current could interfere with and prevent the proper operation of an IONM.